Tides

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Tides

• Essential Question
• What causes tides in the oceans?

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What are Tides?

• The daily rise and fall of Earths waters on its
  coastlines are called tides.
• As the tide comes in, the level of water on the
  beach gradually rises
• As the tide goes out, water flows back to the sea
• Unlike surface waters, tides happen regularly no
  matter how the wind blows.
• Tides occur in all bodies of water, but are most
  noticeable in the oceans and large lakes

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What causes Tides?

• Tides are caused by the interaction of Earth, the
  moon, and the sun
• How?
• Gravity!
• Gravity is the force exerted by an object that
  pulls other objects toward it.
• As the distance between objects increases, the
  pull of its gravity weakens

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What causes Tides?

• The moon pulls on the water on the side of Earth
  closest to it more strongly that it pulls on the
  center of Earth
• This pull creates a bulge of water called a tidal
  bulge on the side of Earth facing the moon.
• The water farthest from the moon is left
  behind, forming a second bulge

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Tides are more influenced by the gravitational
effect of the Moon than they are by that of the
Sun (the Moon's closeness to us outweighs by far
the Sun's greater size).
Low Tide
Moon
Earth
High Tide
High Tide
So, as the Earth spins around its axis, how
many high and low tides do we have a day?
Low Tide
Sun
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Bay of Fundy
The Bay of Fundy in Canada is noted for the great
differences between its high and low tides.
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How does the Sun affect Tides?

• The Sun also causes tides on the Earth, but they
  are smaller than the Lunar tides.
• When the Moon and Sun are aligned, their tidal
  forces combine, and the resulting tides are
  largest.

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What are Spring Tides?

• Twice a month, at the new moon and the full moon,
  the sun and the moon are lined up,
• Their combined gravitational pull produces the
  greatest difference between the heights of the
  tides
• Results Higher High Tide and Lower Low Tide

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What are Neap Tides?

• When the sun and the moon are at right angles to
  each other it produces a neap tide
• This acts to even out the water level over
  Earths surface decreasing the difference between
  high tide and low tide
• Results Lowest High Tide and Highest Low Tide

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